1. Field of the Invention
The present invention relates to signal separation devices, and specifically relates to signal separation devices including a first passband and a second passband adjacent to each other.
2. Description of the Related Art Japanese Unexamined Patent Application Publication No. 2008-271230 discloses a signal separation device that includes a transmission filter and a reception filter connected to an antenna and that has a configuration in which a ground potential connected to the reception filter is isolated from other ground potentials.
Japanese Unexamined Patent Application Publication No. 2010-109894 discloses a ladder-type signal separation device that has a transmission filter and a reception filter and that has a configuration in which a single parallel-arm resonator is used as a notch filter, thereby suppressing a sub-resonant response in the sub-resonant frequency band of the transmission filter or reception filter.
In the invention disclosed in Japanese Unexamined Patent Application Publication No. 2008-271230, routing of wiring lines for isolating the ground potentials from each other is necessary and the arrangement of ground electrodes is restricted. As a result, there may be a case in which it is difficult to reduce the size of the signal separation device.
In the invention disclosed in Japanese Unexamined Patent Application Publication No. 2010-109894, a sub-resonant response is suppressed in the sub-resonant frequency band which is relatively widely spaced apart from the passband of the transmission filter or reception filter. However, when the passband of the transmission filter and the passband of the reception filter are close to each other, the isolation characteristics between the transmission filter and the reception filter are degraded in some cases.